This is Steven Salzberg's blog on genomics, pseudoscience, medical breakthroughs, higher education, and other topics, including skepticism about unscientific medical practices. Here's where I can say what I really think about abuses and distortions of science, wherever I see them.

The bottom line: a daily glass of white wine carries a 13% increased risk of melanoma, one of the deadliest forms of skin cancer. Surprisingly, though, red wine did not carry the same risk. In fact, when the authors separated out beer, red wine, white wine, and other forms of alcohol, only white wine carried any risk for melanoma.

Should you cut back on white wine based on this new finding? I read the study to find out more.

The new study, led by Eunyoung Cho from Brown University, appeared in the most recent issue of a journal published by the American Association for Cancer Research. It's a large, carefully-done analysis of survey information from over 210,000 health professionals, about two-thirds of them nurses, followed over an 18-year period. The 210,000 participants came from 3 studies: 2 studies of nurses and one of male health professionals. About three-quarters of the participants were female, and the vast majority were white (which means the findings might not apply to non-white populations).

One feature I always look for in an analysis like this is a dose-response effect. If the effect is genuine, then higher doses (in this case, more alcohol) should increase the risk. The authors here found that people who drank the most alcohol had the greatest increase in risk. The study also controlled for all the usual confounding factors, such as family history of cancer and smoking.

In some subgroups–those who drank the most white wine–the increased in relative risk of melanoma was 50% or more. Keep in mind, though, that this is "relative risk." I'll get to that in a minute.

When the researchers looked at where the cancer occurred, they found that the risk of melanoma was "far greater" on areas of the body that don't receive regular sun exposure, such as the stomach and back, compared to the arms or neck where people get the most sun. This result suggests that the effect of alcohol is unrelated to sun exposure.

There are several important caveats about this study. Perhaps the biggest is that the mechanism is unclear: how does white wine cause melanoma? The authors suggest that the effect is due to acetaldehyde, a cancer-causing compound that is present in wine. However, both red and white wine contain this compound, so it's not clear why white wine would carry a greater risk. It's also not clear why acetaldehyde should cause skin cancer more than other cancers, and why it should be associated with skin cancer specifically on areas of the body that are not exposed to the sun.

Before you panic, let's revisit the actual amount of risk here. The 13% increase in risk does not mean that you have a 13% chance of getting melanoma from drinking white wine. I looked at the raw numbers in the study, and the overall rate of melanoma in non-drinkers (about 71,000 people in this study) was 0.61%. About 26,000 people reported drinking 10-20 grams of alcohol per day (the equivalent of 1 or more glasses of wine), but the study didn't report how many of these people drank white wine. Nonetheless, in this group the rate of melanoma was 0.85%. So in raw numbers, the increased risk for melanoma was 0.24%.

That's a rather small number, but it's still worrisome. The National Cancer Institute warns that alcohol is linked to several types of cancer (although not melanoma), especially for those who drink excessively. The new study reinforces that warning, and suggests that for those who drink wine, red wine might carry fewer risks than white.

I'm still a bit skeptical, because we have no good explanation for why white wine–but not red wine, beer, or alcohol–would cause skin cancer. But still, when you reach for a glass of wine this holiday season, perhaps you should choose red instead of white.